1. Field of the Invention
The present invention relates to a digital light processing (DLP) projector. More particularly, the present invention relates to a DLP projector without any special optical component such as the conventional Philip prism.
2. Description of Related Art
In a conventional digital light processing (DLP) projector, a key component called “digital mirror device” (DMD) is the fundamental semiconductor component, which is controlled by two-bit pulse modulation. The chip of the digital mirror device is adopted for controlling the digital optical switch by rapidly and precisely reflecting the light source. Unlike the conventional liquid crystal projector that modulates the light by using liquid crystal (LCD) to change the polarization state, DLP projector uses the reflection of micro mirrors to modulate the light. Therefore, the weight of the DLP projector may be reduced to 2.5 kg or less, compared with 8 to 15 kg of a conventional projector. In addition, the volume of the DLP projector can also be minimized. In general, the optical efficiency and contrast of the DLP projector is better than that of the conventional projector, since the digital mirror device uses non-polarized light and switches light by mirrors. Therefore, the DLP projector can be used when high brightness and high resolution is required. In addition, the image reproduced from the DLP projector is a real and stable digital image with correct colors.
FIG. 1 is a schematic plan view of the internal of a conventional DLP projector. As shown in FIG. 1, a conventional DLP projector includes a light source 111, a rod integrator 112, a lens set 113, a reflection mirror 115, an optical splitter and combiner module 120, and a projection lens 119. Wherein, the light 11 is emitted from the light source 111, and is condensed on the reflection mirror 115 via the rod integrator 112 and the lens set 113.
Please refer to FIG. 1. The conventional optical splitter and combiner module 120 includes a total internal reflection (TIR) prism 117 and a Philips prism 121. After the light 11 is reflected from the reflection mirror 115 to the total reflection plane 117a of the TIR prism 117, the incident angle A1 of the light 11 being incident to the total reflection plane 117a is larger than the critical angle of total reflection. In addition, the light 11 penetrates from an optically dense medium to an optically less dense medium since an air gap is located between the two prisms 31 and 32 of the TIR prism 117. Therefore, the light 11 is totally reflected from the total reflection plane 117a into the Philips prism 121.
The Philips prism includes two dichroic coatings, wherein coating 118a reflects the red color light 13 of the light 11 and allows transmission of other color lights, and coating 118b reflects the blue light 15 of other color lights transmitted from the coating 118a, and allows transmission of the green light 17. Accordingly, after the light 11 passes through the Philips prism 121, the light 11 is separated into the red color light 13, the green color light 17, and the blue light 15. Three color lights 13, 15 and 17 are incident to the digital mirror devices 121, 122, and 123 in specific incident angles respectively.
The red color light 13, the green color light 17, and the blue light 15 are incident to the digital mirror devices 121, 122, and 123 are reflected respectively. The reflected red color light 13, green color light 17 and blue light 15 represent the red image, the green image and the blue image respectively. Finally, the red image, the green image and the blue image are incident to the total reflection plane 117a. At this moment, since the incident angle A2 of the red image, the green image and the blue image being incident to the total reflection plane 117a is smaller than the critical angle of total reflection, the red image, the green image and the blue image will penetrate the total reflection plane 117a of the TIR prism 117 directly. Therefore, the red image, the green image and the blue image are projected via the projection lens 119.
In the conventional DLP projector, the light from the light source is not separated into the red color light, the green color light, and the blue light before it is incident to the Philips prism. The Philips prism splits the light from the light source. However, the heavy Philips prism occupies most weight in the whole DLP projector. In addition, the light path in the Philips prism is too long and complex since the Philips prism includes optical splitters and optical combiners. Therefore, when the light travels in the Philips prism, the deformation due to, for example, thermal expansion or reduction may alter the physical property of the lights. As a result, the quality of the projected image is poor. In addition, the digital mirror device needs to be disposed beside the Philips prism in a specific angle, which occupies a lot of space that the whole volume and thickness of the projection device can not be reduced.